1. Field of the Invention
The present invention relates to a technique for image enlargement performed by an image processing circuit.
2. Description of the Background Art
Image pickup elements, such as CCDs, CMOSs and the like which are used in digital cameras and the like, perform photoelectric conversion of light received through color filters, to output pixel signals. Such color filters include RGB color filters, YMCK color filters and the like. From a single-chip image pickup element, a pixel signal for one color is outputted per pixel. For example, when the RGB color filter is used, a pixel signal for one of R (Red) component, G (Green) component and B (Blue) component is outputted for one pixel.
For this reason, as to the pixel signal outputted from the single-chip color image pickup element, interpolation of pixel signals for other color components has to be performed. Various algorithms are used to perform such interpolation, and one of these algorithms uses a correlation value. In this algorithm, the respective degrees of correlation in horizontal and vertical directions are calculated and pixel interpolation is performed by using pixels in the direction where the degree of correlation is higher. Also in Japanese Patent Application Laid Open Gazette No. 2006-186965, pixel interpolation is performed in consideration of the correlation direction.
An image processing circuit in a digital camera and the like also performs enlargement of an image. The image processing circuit enlarges the image by using bilinear interpolation and the like. Though various algorithms can be used to perform such enlargement, interpolation is certainly processing based on prediction. Therefore, it is necessary to perform a filtering process on the enlarged and interpolated image, in order to improve the quality of the image.